Calculated Field: CASE for the sum total number of transactions for a few specific product SKUs

I have a couple of product SKUs (one is a base, the other base+accessory), that have a software subscription service on top of revenue from the hardware. I want to create a couple of calculated fields.

1. The total # of transactions of these specific products SKUs only

2. (The total # of transactions of these specific products SKUs only) * (LTV)